World number one Rafael Nadal has pulled out of the Brisbane International tournament, less than three weeks ahead of the start of the Australian Open.

The 31-year-old had already withdrawn from the Mubadala World Tennis Championship in Abu Dhabi and has now opted not to play in the Brisbane International in the first week of next month as he recovers from a knee injury.

"I am sorry to announce I won't be coming to Brisbane this year," the Spaniard posted on Twitter. "My intention was to play but I am still not ready after last year's long season and the late start of my preparation.

"I had a great time there [in 2017] and it was a great start to the month I spent in Australia. I will be seeing my Aussie fans when I land on the 4th in Melbourne and start there my preparation for the Australian Open."

Nadal was defeated in the final of this year's Australian Open tournament by long-time rival Roger Federer.

Next year's tournament gets underway in Melbourne on January 15.